A Russian national was arrested Wednesday on child pornography charges after his arrest last year outside the Beacon Hill home of Secretary of State John Kerry led to a search of his laptop computers, local and federal officials said.

Vladimir Romanov, 30, was charged with six counts of possession of child pornography.

Romanov was arrested on July 14, 2013, when he parked his vehicle in a no-parking zone outside Kerry's home and began taking pictures of a window in Kerry's Louisburg Square townhouse, authorities said.

A search of his car discovered a modified Ruger pellet gun that was found to be loaded with a carbon dioxide cartridge, prosecutors said.

Romanov allegedly refused to identify himself when confronted by federal agents and was subsequently arrested by Boston Police officers on a charge of drinking alcohol in public.

"After his arrest, Romanov allegedly made statements indicating his involvement in a plot against the U.S. official (Kerry)," the Suffolk County District Attorney's Office said in a statement. No information was released on the nature of the alleged plot.

Diplomatic Security agents obtained a warrant to search two computers found inside Romanov's home and discovered sexually explicit images of children on the hard drive of one laptop computer and multiple "specimens" of what authorities allege to be child pornography.

Romanov was ordered held on $25,000 bail at his arraignment in Suffolk Superior Court.